Porth's Essentials of Pathophysiology, 4e

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Musculoskeletal Function

U N I T 1 2

Angular andTorsional Deformities All infants and toddlers have lax ligaments that become tighter with age and assumption of the weight-bearing posture. The hypermobility that accompanies joint laxity coupled with the torsional, or twisting, forces exerted on the limbs during growth are responsible for a number of variants seen in young children. Torsional forces caused by intrauterine positions or sleeping and sitting patterns twist the growing bones and can pro- duce deformities as a child grows and develops. In infants, the femur normally is rotated to an ante- verted or forward position with the femoral head and neck rotated anteriorly with respect to the femoral con- dyles. Normally this angle is approximately 40 degrees at birth and declines to 15 to 29 degrees by 8 to 10 years of age. 55 A second source of rotation is found in the tibia. Infants can have 30 degrees of medial rotation of the tibia, and by maturity the rotation is between 5 degrees of medial rotation and 15 degrees of lateral rotation. 55 Abnormalities of rotation may include excessive adduc- tion (turning in or toward the body) or abduction (turn- ing out or away from the body). Intoeing and Outtoeing. The foot progression angle describes the angle between the axis of the foot and the line of progression. 55 It is determined by watching the child walking and running, although it is usually less noticeable when the child is running or barefoot. Figure 43-13 illustrates the position of the foot in intoeing and outtoeing. Inward rotation of the foot is assigned a negative value and outward rotation is assigned a positive value. The normal value in children and adolescents is 10 degrees (range −3 to 20 degrees).

 Skeletal Disorders in Children

During childhood, skeletal structures grow in length and diameter and sustain a large increase in bone mass. Alterations inmusculoskeletal structure and functionmay develop as a result of normal growth and developmental processes or as a result of impairment of skeletal develop- ment caused by hereditary or congenital influences.

Variations of Normal Growth and Development

Infants and children undergo changes in muscle tone and joint motion during growth and development. Intoeing, outtoeing, bowlegs, and knock-knees occur frequently in infancy and childhood. They usually cause few problems and are corrected during normal growth processes. The normal folded position of the fetus in utero causes phys- iologic flexion contractures of the hips and a froglike appearance of the lower extremities (Fig. 43-12). The hips are externally rotated and the patellae point out- ward, whereas the feet appear to point forward because of the internal pulling force of the tibiae. During the 1st year of life, the lower extremities begin to straighten out in preparation for walking. Internal and external rota- tions become equal, and the hips extend. Musculoskeletal assessment of the newborn is impor- tant to identify abnormalities that require early inter- vention, facilitate treatment, establish baselines for future reference, and educate and counsel parents. 53–56 There are many clinical deviations that are easily cor- rectable in a newborn. Many others correct spontane- ously as the child grows.

A

B

Foot progression angle

Line of progression

C

FIGURE 43-13. (A) Intoeing, (B) outtoeing, (C) intoeing and outtoeing can be determined by watching a child walk and comparing the long axis of the foot with the direction in which the child is walking. If the foot is directed inward, the angle is negative and indicative of intoeing; if it is positive, it is indicative of outtoeing.

FIGURE 43-12. Position of fetus in utero, with tibial bowing and legs folded. (From Dunne KB, Clarren SK.The origin of prenatal and postnatal deformities. Pediatr Clin North Am. 1986;33(6):1277–1297; with permission from Elsevier Science.)